Traditionally, most hearing aids capture sound through a microphone that is located inside or on top of the pinna of the ear, and deliver an amplified and/or modified version of the sound signal into the user's ear canal through a suitable electrical-to-audio transducer, e.g., a small speaker. Disadvantageously, the proximity of the microphone to the transducer poses the potential problem of feedback from the transducer to the microphone.
The solution in the past for eliminating feedback has been to occlude the ear canal via an ear mold such that the transducer is located distally to the occlusion, while the microphone is located proximally to the occlusion. Unfortunately, occlusion of the ear canal can create several disadvantages for the user, such as reverberation and physical discomfort, and is a major cause for non-use of traditional hearing aids by the hearing impaired.
In addition, it is desirable to make hearing aids less visible, as most users perceive the aid as imparting a negative stigma. Thus, hearing aids are continuously becoming smaller and have moved from behind the ear into the outer ear and into the canal of the ear.
It is known in the art to connect the retro-auricular space (space behind the pinna of the ear) to the ear canal via a hollow titanium tube that is permanently placed into soft tissue. See, e.g., U.S. Pat. No. 6,094,493, which patent is incorporated herein by reference. In one embodiment presented in the '493 patent, an amplification hearing aid is connected to the proximal (retro-auricular) end of the tube, whereby the hearing aid is located behind the pinna of the ear and a transducer sends the amplified sound signal through the tube into the ear canal. This concept, which has been commercialized by Auric® Hearing Systems, Inc. of Charlotte, N.C. as the RetroX technology, allows a certain degree of amplification without feedback and without the need for occlusion of the ear canal. In another embodiment of the '493 patent, the microphone, transducer, electrical and electronic components are installed in the tube. The existing technology suffers from infection and inflammation in the area of the tube, among other things.
Several concepts for implanting all or part of the hearing aid into the middle ear have been developed. Such approaches couple an amplified and processed version of the sound signal to structures of the middle ear mechanically, thereby reducing feedback without occlusion of the ear canal. Such systems also reduce or eliminate visibility of the hearing aid, and have the potential for improving user comfort. Disadvantageously, however, such middle-ear-coupled systems require, inter alia, a significant surgical procedure.
In U.S. Pat. No. 5,430,801, the use of a silicone tube is disclosed to direct the output of a conventional hearing aid, held in place behind the ear using an ear-hook or via a piercing through the cartilage of the pinna, into the ear canal. One embodiment disclosed in the '801 patent contemplates placing the distal end of the tube in the middle ear to achieve better gain. However, such embodiment, like all middle-ear devices, involves a significant surgical procedure, and the risk of infection is much greater than a simple piercing of the soft tissue behind the ear. Further, the microphone associated with the hearing aid disclosed in the '801 patent is held at the front of the pinna, either as part of the piercing or connected to the hearing aid through an earring-type coupler.
It is thus seen that what is needed is a hearing aid that is less visible, smaller, and which is positionable so that part or all of the hearing aid is recessed or implanted in the body so as to be largely invisible, and which does not occlude the ear canal. Moreover, what is needed is such a hidden, non-occluding hearing aid that can be readily removed for battery recharging or replacement. Furthermore, such a hearing aid should provide protection from infection and/or inflammation in the area of the aid.